Iron-chromium titanium base alloys



United States Patent IRON-CHROMIUM TITANIUM BASE ALLOYS Schuyler A. Herres, Albany, and Thomas K. Redden, Cohoes, N. Y., assignors to Allegheny Ludlum Steel Corporation, Brackenridge, Pa., a corporation of Pennsylvania No Drawing. Application February 8, 1950,

Serial No. 143,148 v 11 Claims. (Cl. 75175.5)

This invention relates to new and improved titaniumbase alloys containing iron and chromium and a hardening element of the type of oxygen and nitrogen and particularly, to a titanium-base alloy which has greatly improved tensile and yield strengths, adequate ductility for hot and cold forming, excellent corrosion resistance, and which may be reversibly hardened or softened by proper heat treatment.

This application is a continuation-in-part of our application, Serial No. 118,723 entitled Titanium Alloys and filed September 29, 1949.

An alloy of the type here involved is particularly suitable for structural uses, such as aircraft engines, frames, turbines, etc., where higher strength and light Weight are essential. The alloy has a substantially uniform crystalline structure that can be fully developed by hot and cold working operations and heat treatment. It also has a high corrosion resistance, particularly against sea water and chloride solutions.

An object of our invention has been to provide ti-' tanium-base alloys for structural purposes having a good load carrying ability and sufiicient ductility for working, etc.

The constituents of the alloys fall within the following exemplary ranges: i

For optimum results in alloy A, the iron should be a minimum of about 2 times the oxygen content and not substantially less than and about /2 the amount of chromium content (at least about 1 iron to 2 chromium). The oxygen is used within a range permissible and is proportioned to the chromium and iron to provide hardening without excessive hardness.

For optimum results in alloy B, the iron should be a minimum of about 4 times the nitrogen content and not substantially less than and about /2 the amount of Like the oxygen of A, the nitrogen chromium content. is used within a range permissible and is proportioned to the "chromium and iron to provide hardness withoutexcessive hardness.

In alloy C, where both oxygen and nitrogen are used, their ranges are substantially the same as where they are used separately, see alloys A and B. The lower limits of the iron and chromium are substantially the same as before,but their upper limits are slightly greater, although the /2 to 1 ratio is maintained for optimum results.

The following alloys represent alloys within the ranges of Table I which distinguish from each other from the standpoint that the second set A2, B2 and C2 make possible the retention of a body-centered lattice structure:

'TABLE H Percent O .02 to .50 Fe .75 to 3.0 Cr 1.5 to 6.0

Per cent N .10 to .25 Fe .75 to 3.0 Cr 1.5 to 6.0

C1 Per cent 0 .02 to .50 N .02 to .25 Fe .75 to 3.0 Cr 1.5 to 6.0

- Per cent 0 .02 to .50' Fe 4.0 to 7.0 Cr 8.0 to 14.0

Per cent N .05 to .20 Fe 4.0 to 7.0 Cr 8.0 to 14.0

Per cent 0 .02 to .50 N .02 to .25 Fe 4.0 to 7.0 Cr 8.0 to 14.0

The following is representative of properties attained inan alloy of the typehereinvolved which has beenforged and annealed-at temperatures in the range of 1200-1600 F.-for one hour, and cooled in air:

TABLE III Alloy Addition, percent Hard Tensile ield Elon ness, Strength, Strength, i'i O N or Fe BHN p. s. 1. p. s. l.

3 Representative optimum oxygen-containing alloys of Table III, namely 1, 3, 6 and 8 to 13, inclusive, fall within the following range:

TABLE IV Percent O .05 to .50 Fe 1 to '5 Cr 2 to 10 Representative optimum nitrogen-containing alloys of Table III, namely 14 to 20, inclusive, fall within the following range:

TABLE V Per cent .10 to .25 1 to 4.8 2 to 10 N Fe Cr Representative optimum oxygen and nitrogen containing alloys 'of Table III, namely 2, 4, 5 and 7, fall within the following range:

TABLE VI Per cent perature.

TABLE VII Examples of response of A, B, C type alloys to heat .25% O, 2.7% Cr, 1.3% Fe 105% o, 2.7% CI", Heat Treatment Fe BHN Hardness BHN Hardness hr.+water'quench. hr.l.water queneln hr.+water quench. hr.+water quench. hr. -l water quench F 54 hr.+wa'ter quenchy hn-i-alr cool Alloys A2, B2 and Oz respond favorably to heat treatment of a difierent type. That is, on heating to a temperature somewhat above 1400" F. and cooling at a rate that may be slower, the higher the content of chromium and iron or both of them, a high temperature bodycentered cubic lattice structure characteristic of titanium at higher temperatures is stabilized and retained at room temperature. This produces a softer more ductile alloy than if the, same alloy were cooled sufficiently slowly to transform it into a hexagonal, closely-packed lattice structure.

' All of the alloys may be hardened somewhat bymoderately rapid cooling from a temperature above about 1200 E, followed by an aging or precipitation hardening mechanism on reheating and holding for various periods within the temperature range, of 500 to. 1000 F; The time of holding is less, the higher the aging temperature in this range and the effect is reversible, so that the alloy may be softened againby reheating to a higher temperature.

All ofi the alloys may also be hardened by cold working,

as by mechanical reduction in cross-sectional area at temperatures belOW about 12U0 F. and may be 'Sbftild again by heating to temperatures above about 1200 F. for various periods, the temperature and time employed in the softening operation will depend on the degree of cold work accomplished. They may also be surface hardened as pointed out in the above-entitled co-pending application.

The small amounts of oxygen and nitrogen appear beneficial in improving the properties of the body-centered alloys A2, B2 and C2. In these alloys, the body-centered structure is assured by water quenching where the alloys contain chromium from about 8 to 14% and iron from about 4 to 7%, although air cooling may be employed where the chromium or iron or both of them are in higher amounts of the ranges. For example, an alloy containing about .15% iron, about .02% nitrogen, about .1% oxygen, and about 10% chromium will retain the body-centered structure on water quenching, but not on air cooling; if the chromium content is about 14%, the structure will be retained on air cooling. An alloy of about 4.8% iron, 10% chromium with about 2% nitrogen and .1% oxygen will retain the structure on air cooling. It is thus seen that the combination of iron and chromium favors retention of the body-centered structure.

The alloys of our invention are economical from the standpoint of the chromium used and excessive hardness and non-uniform characteristics are avoided by maintaining the three alloying additions Within the ranges specified and especially in this respect, such proportions are critical, and particularly as to the maximum percentages of the oxygen, nitrogen and iron.

- From the above it will be apparent that the specified range of nitrogen has a comparable effect to the specified range of oxygen, that the maximum amount of nitrogen has to be maintained below that of a comparable amount of oxygen, and that this is also true when the two gases are used in combination in an alloy of our invention. As compared to alloy A which contains oxygen and has a minimum iron content of about 37 times the minimum exygen content, alloy B which contains nitrogen has a minimum iron content of about fifteen times the minimum nitrogen content; the ranges of the iron and chromium are the same in both cases. However, when both gases are used, see alloy C, the minimum amount of iron is proportional by the first specified amount to either the minimum oxygen or minimum nitrogen content. In addition, the, ranges of the chromium and iron are slightly greater than when either of the gases is used alone.

TABLE VIII Results 0 comparativ-e stress rupture tests COMMEROIALLY PURE TITANIUM [75,000 p. s. i. tensile strength] 800 -F 30 000 p. s. l Broke on Loading. 39% E1ong., 78%

Red. Area. 800 F. 10,000 p. s. i- 340 Hrs 17% Elena, 71%

. Bed. Area.

TITANIUM ALLOY [25% 0, 2.7% Cr, 1.3% Fe] 500 F 05,000 p. s 3,050 hrs (22%, Elong, still; go.- 12. 700 F 65,000 p. S. l 1,901 hrs (2.5% Elong, still i g.) 800 F, 30,000 p. s. l 2,248 hrs. (re- (2.7% Elong, 3.1%

' moved). Red. Area. 00- F 30,000 p. s. i 2,557 hrs. (3 6% Elong., still go- 1T17 81,000 E 20,000p. s. i 13.5 hrs (47.70 Elong 94% Red. Area. 1,000 F 20,000 p. s. l 13.5 hrs (442% Elongt, 92%

Red. Area.)

Properties of discs such as would be used for jet aircraft compresser wheels:

TENSILE PROPERTIES FOR TITANIUM ALLOY DISCS 7-inch diameter titanium alloy (15% O, 2.7 Cr, 1.3% Fe) ingot Disc upset from a two inch square inches high to one inch thick 6 inch diameter. Forging was done at 1700 F. on a 2000 lb. hammer in one heating. Disc was annealed for one hour at 1300 F. after forging. Standard A inch diameter test specimens were taken from the chord and on a diameter at the center of the disc.

Ultimate Strength Elong. 1" Red. Area Chord 1- 129, 000 25 51 Chord 2- 131, 400 20 51 Center 3.--- 131, 000 24 58 12-inch diameter titanium alloy (.25% O, 2.7% Cr. 1.3% Fe) Ingot t iig i f s. 1" Red. Area What we claim is:

1. A titanium base alloy which contains iron within a range of about .75 to chromium within a range of about 1.5 to 20%, at least one gas within the ranges specified from the group consisting of: oxygen about .02 to .50% and nitrogen about .02 to .25%; the balance titanium with incidental impurities, and the chromium, iron and at least one of the gases being essential elements with the titanium.

2. A titanium-base alloy for structural purposes consisting essentially of about .75 to 10% iron, about 1.5 to 20% chromium, at least one alloying gas within the ranges specified from the group consisting of: oxygen about .02 to .50% and nitrogen about .02 to .25%; the balance titanium; the iron being maintained within a minimum of about two times the oxygen content, about four times the nitrogen content, and within a ratio of not less than about one half the chromium content.

3. A titanium-base alloy for structural purposes having a minimum tensile strength after annealing of about 110,000 p. s. i. and which consists essentially of about .75 to 10% iron, about 1.5 to 20% chromium, at least one alloying gas within the ranges specified from the group consisting of: oxygen about .02 to .50% and nitrogen about .02 to .25%; and the balance titanium.

4. A titanium-base alloy suitable for structural purposes which contains iron within a range of about .75 to 7%, chromium within a range of about 1.5 to 14%, and at least one gas within the ranges specified of the group consisting of oxygen about .02 to .50% and nitrogen about .02 to .25 and the balance titanium with incidental impurities.

5. A titanium-base alloy suitable for structural purposes which contains iron within a range of about .75 to 10%, chromium within a range of about 1.5 to 20%, nitrogen within a range of about .02 to .25 oxygen within a range of about .02 to .50%, and the balance titanium with incidental impurities.

6. A titanium-base alloy suitable for structural purposes which contains iron within a range of about .75 to 3%, chromium within a range of about 1.5 to 6%, at least one gas within the ranges specified of the group consisting of oxygen within a range of about .02 to .50% and nitrogen within a range of about .02 to .25%, and the balance titanium with incidental impurities.

7. A titanium-base alloy suitable for structural purposes which contains iron within a range of about 4 to 7%, chromium within a range of about 8 to 14%, at least one gas within the ranges specified of the group consisting of oxygen about .02 to .50% and nitrogen about .02 to .25 and the balance titanium with incidental impurities.

8. A titanium-base alloy suitable for structural purposes which contains iron within a range of about 1 to 5%, chromium within a range of about 2 to 10%, at least one gas within the ranges specified of the group consisting of oxygen within a range of about .05 to 50% and nitrogen within a range of about .10 to .25 and the balance titanium with incidental impurities.

9. A titanium-base alloy suitable for structural purposes which contains iron within a range of about 1 to 6.5%, chromium within a range of about 2 to 13%, oxygen within a range of about .05 to .25 about .05% nitrogen and the balance titanium with incidental impurities.

10. A titanium-base alloy suitable for structural purposes which contains about 1.3% iron, about 2.7% chromium, about .15 to 25% oxygen, and the balance titanium with incidental impurities.

11. A titanium-base alloy consisting of from 2-5% chromium, from 12% iron, from .05-20% nitrogen and the balance titanium.

References Cited in the file of this patent Product Engineering, Nov. 1949, page 150.

Modern Metals, March 1950, page 37.

Titanium Report of Symposium, Dec. 16, 1948, sponsored by Ofiice of Naval Research, Dept. of the Navy, pages 73 and 74. 

1. A TITANIUM BASE ALLOY WHICH CONTAINS IRON WITHIN A RANGE OF ABOUT .75 TO 10%, CHROMIUM WITHIN A RANGE OF ABOUT 1.5 TO 20%, AT LEAST ONE GAS WITHIN THE RANGES SPECIFIED FROM THE GROUP CONSISTING OF: OXYGEN ABOUT 0.2 TO .50% AND NITROGEN ABOUT .02 TO .25%; THE BALANCE TITANIUM WITH INCIDENTAL IMPURITIES, AND THE CHROMIUM, IRON AND AT LEAST ONE OF THE GASES BEING ESSENTIAL ELECMENTS WITH THE TITANIUM. 